Chapter 7: Sedimentary Rocks Flashcards
What are sediments?
Any solid that settles to the bottom of a liquid
What are detrital sediments?
Particles derived from weathering of pre-existing rocks
Transported a distance from its source
What are chemical sediments?
Precipitate or are extracted by organisms
Forms where is deposits
What are sedimentary rocks?
Composed of sediments
Make 5% of the crust
Host for many resources
(Oil, gas) banded formations
What is the procedure to make sedimentary rocks
Weathering, erosion, sediment transportation
What are the particle sizes?
Biggest to smallest:
Gravel Sand Silt Clay Mud
What is sorting?
Size distribution of particles
Poor: particles of different sizes
Well: particles same size
How does sediment become sedimentary rocks?
Through lithification
Compaction: volume of sediments decrease weight of overlying sediment causes a reduction in pore space as particles pack more closely together
Cementation: glues the sediments together.
The most common cements:
Calcium carbonate and silica
Calcium carbonate readily dissolved in water with carbonate acid. Chemical weather of felspar yield silica solution
Names the detrital sedimentary rocks.
Classic texture
- Conglomerate- gravel sized particles, rounded
- Breccia- gravel sized particles, angular
- Sandstone- sand sized particles, classified based on mineral content
- Mudrock- silt and Clay - sized particles
i siltstone: silt
ii mudstone: mixture of silt and Clay
iii clay stone: Clay
iv shale. Fissile (break along parallel planes)
What are biochemical sedimentary rocks?
Produced by the chemical activity of organisms
Substances derived from solution by inorganic or biochemical processes
What are the two textures of sedimentary rocks?
Crystalline- composed of mosaic of interlocking crystals
Classic- made up of fragments (sea shells flies together)
What are the carbonate rocks?
Limestone- don’t need to scratch to react
Coquina limestone- fragmented seashells
Oolitic limestone- composed of ooids
Dolostone- forms when mg replaces some ca in limestone (scratch to react)
What are the evaporates?
Halite
Gypsum
Chert- flint - dark chert
Jasper- red chert
Bitchomous coal
What if peat?
Partially decayed plant remains found in low-oxygen waters
Converts from lignite - bitumous coal - anthrocite (99% carbon)
What is sedimentary facies?
Bodies of sediment each possessing distinctive physical, chemical and biological attributes
What are examples of sedimentary facies?
Marine transgression- sea level rises; shoreline moves inland
Marine regression- sea level falls; shoreline moves seaward
Name and explain the 3 kinds of sedimentary structures (bedding)
Strata beds- layers of rocks
Cross bedding- angles angles with respect to depositional surface (ripple currents)
Graded bedding- upward decrease in grain size (turbidity current)
(Look at figures you made)
Name and explains 5 more sedimentary structures
Ripple marks- small scale alternating ridges and troughs
Current ripple marks- streams leave behind asymmetric ripple marks
Waves- shallow marine ripple marks have a symmetrical shape from the rocking motion of the waves
Mud cracks- subjected to periodic drying
Fossils
How to determine the environment of deposition?
Consider texture and other sedimentary structures
Use your understanding of natural processes, the principle of uniformitarianism (fossils in the Rockies)
ex. Navajo sandstone firmed as ancient sand dunes
How are petroleum and natural gas form? (Hydrocarbon)
Micro organisms die in low oxygen bottom of seas of large lakes
The lack of oxygen prevent totally decay
Organic sediments are buried (temp must be just right)
Low density oil and/or natural gas migrates upward from the source rock
May reach the surface or accumulate in reservoir rocks underneath traps
Stratigraphic traps form cause of facies changed in rock layer
Structural traps form as the result of folding of fracturing (faulting) of rocks
What is banded iron formation?
Alternating thin layers of chert and iron minerals, mostly iron oxides (hemitite, megnitite)
Nearly all of earths iron ore is mined from them
